DECLARING SHEVISAH WHEN ON THE ROAD
(Mishnah): If he said 'my Shevisah is at the trunk', he may walk 2000 Amos to the tree, and another 2000 Amos from the trunk to his house, 4000 Amos in all after dark.
(Rava): This is only if [when he declared his Shevisah] had he run, he would have reached the tree before dark.
Question (Abaye): The Mishnah says 'it was dark for him'!
Version #1 - Answer (Rava): It was dark (too late) for him to reach his house [before Shabbos], but it was not dark for him to reach the tree.
Version #2 - Answer (Rava): It was dark (too late) for him to get there walking slowly, but if he would run, he could reach there.
Rabah and Rav Yosef were walking. Rabah said 'my Shevisah is under the date tree that supports another tree.'
Rav Yosef: I do not know that tree!
Rabah: You can rely on me!
(Beraisa - R. Yosi): If Reuven knew a particular place and Shimon did not, Shimon says that his Shevisah will be with Reuven, and Reuven says 'my Shevisah is at Ploni.'
Really, R. Yosi did not teach the Beraisa. Rabah said it in the name of R. Yosi in order that Rav Yosef would rely on it, for R. Yosi has solid reasons to support his teachings. (Magen Avraham 156:2 - if one knows that the Halachah follows a teaching, he may say it in the name of a great Chacham who did not say it, in order that others will accept it.)
THE SOURCE FOR THE TECHUM OF 2000 AMOS
(Mishnah): If he did not see a fence or tree, or did not know [...and declared his Shevisah in his place, he gets 2000 Amos].
Question: What is the source in Torah for these 2000 Amos?
Answer (Beraisa): "Shevu Ish Tachtav" alludes to four Amos;
"Al Yetzei Ish mi'Mkomo" alludes to 2000 Amos.
Question: How do we learn this from the verse?
Answer (Rav Chisda): We learn "mi'Mkomo" from the Leviyim's cities (each received a Techum of 2000 Amos) through the following chain of words. (There is a Gezeirah Shavah between every pair of identical words. Adjacent words that are different are written in the same verse, so we learn from one to the other): Makom, Makom, Nisah, Nisah, Gevul, Gevul, Chutz, Chutz. (Rashi Shabbos 34a - this is an Asmachta.)
It says "u'Madosem miChutz la'Ir Es Pe'as Kedmah Alpayim ba'Amah." (The other verses in the chain are "... mi'Chutz li'Gvul Ir Miklato", "... Es Gevul Ir Miklato Asher Yanus Shamah", "V'Samti Lecha Makom Asher Yanus Shamah".)
Question: Why don't we learn [a smaller Chidush,] from "mi'Kir ha'Ir va'Chutzah Elef Amah"?
Answer: We learn Chutz from Chutz, and not from Chutzah.
Question: One may learn a Gezeirah Shavah even from different words!
(Beraisa - Tana d'Vei R. Yishmael): [The Gezeirah Shavah] "v'Shav ha'Kohen...; u'Va ha'Kohen" equates the law [of a house with Tzara'as] when the Kohen [first] returns with when he comes [another week later].
Answer: This is when there are no words that are more similar. When there are words that are more similar, we learn from them.
(Mishnah - R. Chanina ben Antigonus): The 2000 Amos are circular.
Question: Either way you say, this is difficult!
If he learns the Gezeirah Shavah [he should agree that the Amos are square, for] it says Pei'os [corners]!
If he does not learn the Gezeirah Shavah, what is his source for 2000 Amos?
Answer: He learns the Gezeirah Shavah. Here is different, for it says "Zeh Yihyeh Lahem Migreshei he'Arim." We give corners here, but not for laws of Shabbos
Question: How do Chachamim expound this?
Answer (R. Chananyah - Beraisa): All laws of Shabbos are 'ka'Zeh' (like this).
(Rav Acha bar Yakov): One is liable for carrying four Amos in Reshus ha'Rabim only if he carried four and its diagonal. (Rashi - if the side of a square is four, the diagonal is about five and three fifths. Rashbam - this applies only to carrying on a diagonal, e.g. northwest. We do not give a diagonal to one who carried [due] north, south, east or west. Surely, this is like Chachamim. R. Chanina ben Antigonus does not give corners for laws of Shabbos.)
Question (Rava): If a pillar in Reshus ha'Rabim is 10 tall and four wide, must the width be four and its diagonal [to be Reshus ha'Yachid, according to Chachamim]?
Answer (Rav Papa and Talmidim - R. Chananyah's Beraisa): All laws of Shabbos are 'ka'Zeh.' (The diagonal is required.)
WHO MAY BE ME'AREV THROUGH WALKING?
(Mishnah): This is like it was taught, that an Oni can be Me'arev through walking. R. Meir says, only an Oni can do so. [R. Yehudah says, the same applies to an Ashir...]
(Rav Nachman): They argue about one who said 'my Shevisah is in my place':
R. Meir holds that Eruv is primarily with bread. Chachamim were lenient only for Aniyim;
R. Yehudah holds that Eruv is primarily through walking, for Aniyim and Ashirim;
If he said 'my Shevisah is in that place', all agree that this works only for an Oni.
Question: In the Mishnah, who taught 'this is like it was taught [that an Oni can be Me'arev through walking]'?
Answer: R. Meir taught it.
Question: To which law does he refer?
Answer: He refers to 'if he did not see a fence or tree, or did not know the Halachah [and declared Shevisah in his place, he gets 2000 Amos].'
Question: Who taught 'an Eruv with bread is a leniency for Ashirim, so they need not walk'?
Answer: R. Yehudah taught it.
(Rav Chisda): They argue about one who said 'my Shevisah is in that place.' R. Meir permits only for Aniyim, and R. Yehudah permits anyone;
If he said 'my Shevisah is in my place', all agree that this works for anyone, for Eruv is primarily through walking.
Question: Who taught 'this is like it was taught [that an Oni can be Me'arev through walking]'?
Answer: R. Meir taught it.
Question: To which law does it refer?
Answer: It refers to 'if it was [getting] dark' [and he declared his Shevisah at the trunk, it works].
Question: Who taught 'an Eruv with bread is a leniency for Ashirim'?
Answer: It is like both of them.
Support #1 (for Rav Nachman - Beraisa - R. Meir): Anyone may be Me'arev with bread;
An Ashir may not leave the Techum and say 'my Shevisah is in that place.' Only one who is traveling and sees that it is getting dark may do so.
R. Yehudah says, anyone may be Me'arev through walking;
An Ashir may leave the Techum and say 'my Shevisah is in that place.' This is the primary Eruv.
Chachamim are lenient for a Ba'al ha'Bayis and permit him to send an Eruv with his slave, son or Shali'ach.
R. Yehudah: A case occurred in which people in certain places used to give out dried figs and raisins to Aniyim [on Shabbos] in years of famine. Aniyim of nearby villages used to go to the end of the Techum just before Shabbos [to be Me'arev] and go to receive.
Support #2 (for Rav Nachman - Rav Ashi - Mishnah - R. Yehudah): If [on Erev Shabbos] Reuven was walking towards another city for which one needs an Eruv to go there, and Shimon met him and persuaded him to go back, Reuven may go there [on Shabbos]. Other people of his city are forbidden.
Question: Why is he different than the rest of his city? (Also he was not Me'arev!)
Answer (Rav Huna): The case is, Reuven has one house here, and another house 4000 Amos away in the other city. He intended to go to his other house, and not to be Me'arev. Therefore he is like an Oni. He can declare his Shevisah to be at the end of the Techum. The rest of his city are Ashirim.
This shows that an Oni can declare his Shevisah to be elsewhere, but an Ashir cannot!
R. Chiya bar Aba (to Chiya bar Rav): Both an Oni and an Ashir...
Rav: Also teach him that the Halachah follows R. Yehudah [according to Rav Nachman, that an Ashir may be Me'arev through walking, but only in his place].